The present invention relates to a pneumatic radial ply tire and to the problem of crown lift-off (upward buckling of the tread) when a tire is inflated, underinflated or in the case of runflat tires, uninflated. More specifically, the present invention relates to tread underlays that serve to stiffen the tread and improve handling behavior, in both non-runflat tires, as well as runflat tires during inflated, underinflated or uninflated operation.
A typical driver can usually feel when the handling of an automobile or light truck deteriorates when one or more tires (non-runflat as well as runflat tires) is underpressurized or underinflated. During underpressurized operation, the area of contact between the road and the tire tread changes in undesirable ways. Most specifically, the central region of the ground-contacting portion of the tread tends to lift off of the ground, or to buckle upwards, thereby reducing the tread""s area of contact with the ground, which affects vehicle handling.
An additional problem associated with underinflated operation is cyclical flexure of the region of the ground-contacting portion of the tire""s crown and sidewalls which, especially during high speed operation, can lead to heating and to fatigue failure of the tire components and structure such that the result can be crown failure of the tire.
The problem of crown lift-off is especially relevant to the design of runflat tires, also known as Extended Mobility Tires (EMTs), which are designed to provide continued operation service when underinflated or even when uninflated.
It is believed that the problem of tread lift-off is also relevant to the design of non-EMTs which can also suffer handling problems when operating in an underinflated mode, especially during high-speed operation when the problem of flexure and flexure-induced heating is greatest.
Therefore the goals of tire design include various structural designs that minimize the upward buckling of the central portion of the ground-contacting portion of the tread so as to enhance vehicle handling in all circumstances including, when the tire is at normal operating pressure, if the tire loses part of its pneumatic pressure or, in the case of EMTs, if the tire looses all of its inflated pressure.
In general, the term xe2x80x9crunflat,xe2x80x9d when applied to an EMT, means that the tire structure alone has sufficient strength to support the vehicle load when the tire is operated in the uninflated condition. That is, the sidewall and internal surfaces of the tire do not collapse or buckle onto themselves in the extreme manner associated with conventional tires that are uninflated. Current EMT design is directed toward providing rigid sidewalls and crown structures, rather than to the incorporation of internal supporting structures and devices to prevent the tire from collapsing. However, design consideration is also often given to the strengthening of the crown region.
Thus, among the goals of improving tire design, both of EMTs and non-EMTs, is that of stiffening the crown region against undesirable flexure during low-pressure or no-pressure operation. Among the ways to stiffen the crown is that of incorporating an underlay beneath the tread, radially inward of the belts and radially outward of the ply layers of the carcass.
For example, Cluzel, in U.S. Pat. No. 5,996,662, describes a xe2x80x9cheavy vehiclexe2x80x9d reinforcement xe2x80x9ccomposed of at least two crossed working plies and at least one ply of circumferential cables arranged above the carcass ply.xe2x80x9d
Colom, U.S. Pat. No. 6,082,426 describes the incorporation of a xe2x80x9ccrown reinforcement having at least two working crown plies made of inextensible cables, crossed from one ply to the other and forming angles of between 10xc2x0 and 45xc2x0 with the circumferential directionxe2x80x9d and xe2x80x9can additional, axially continuous, ply formed of metallic elements oriented substantially parallel to the circumferential direction . . . place radially between the working pliesxe2x80x9d and extending laterally to 1.05 times the width of the breaker(s).
Abe, et al., in U.S. Pat. No. 4,506,718, describe an off-road vehicle tire having an extra layer of reinforced crown material designed to resist penetration by sharp objects.
Costa Pereira, et al., in U.S. Pat. No. 6,199,612, describe a xe2x80x9csingle layer of cushion compound between the cords of the carcass reinforcement that are furthest radially outward in the crown and eh cords of the belting that are furthest radially inward in the crown,xe2x80x9d for the purpose of increasing crown rigidity without sacrificing losses to hysteresis; but no reinforcing cords are evident in this design of Pereira, et al.
Southarewsky, in U.S. Pat. No. 5,759,314, shows a crown reinforcement for a biased ply tire in which the reinforcement consists of xe2x80x9ca member disposed between a first carcass and an additional carcass in the crown region of the tire for restricting the circumferential growth of the tire. The reinforcement member includes a plurality of cords oriented at zero degrees. The total circumferential strength of the reinforcement member is about 20% to 250% of the circumferential strength of the carcass plies.xe2x80x9d
A further goal is to minimize the weight of such crown reinforcements, especially given that, because they are disposed radially distant from the axis of rotation, add to the tire""s rotational moment of inertia about its main axis of rotation, which detracts from vehicle acceleration due to both the excess weight and the increased moment of inertia, as well as heat build up due to flexure of the additional material. The ideal crown stiffening invention has minimal weight. In EMT tires, the sidewall reinforcements tend to convey undesirable bending stresses to the crown region during low-pressure and no-pressure operation, which is also to be resisted by the crown reinforcement so as to give improved tire life under less-than-optimal-pressure operation.
With respect to conventional non-EMT tires, it is believed that the benefits of a crown and tread region that is resistant to upward flexure or liftoff during underinflated operation is, of course, improved vehicle handling during the interval until the tire can be reinflated to full pressure or otherwise repaired and reinflated to full design pressure.
The present invention relates to a pneumatic radial ply tire having a tread, a carcass with two sidewalls, two inextensible annular beads, a radial ply structure, a belt structure located between the tread and the radial ply structure, and an air impermeable innerliner. In addition, a crown stiffening underlay structure is disposed radially inward of and adjacent the belt structure and radially outward of and adjacent the radial ply structure. The underlay structure is comprised of a single flat strip of material disposed in a plurality of spaced apart circumferential windings about the tire carcass. The flat strip is comprised of a plurality of high modulus, essentially inextensible cords embedded more or less parallel to one another within an elastomeric matrix. The high modulus, essentially inextensible cords are made of a material selected from a group of materials exemplified by nylon, rayon, polyester, aramid, metal and glass. The overall lateral width of the underlay structure is less than the lateral width of the breaker structure. The plurality of essentially inextensible cords embedded within the elastomeric matrix of the underlay structure may or may not be cut at regular intervals of between about 10 cm and 20 cm, to enable the underlay strip to increase in length to accommodate the increase in circumference as the green tire carcass is blown up into a toroidal carcass shape. The cords are cut if the blow up change in diameter of the underlay strip is greater than the limited extensibility of the cord.
In a second embodiment, the present invention relates to a pneumatic radial ply tire having a tread, a carcass with two sidewalls, two inextensible annular beads, a radial ply structure, a belt structure located between the tread and the radial ply structure, and an air impermeable innerliner. The tire has a crown stiffening underlay structure disposed radially inward of and adjacent the belt structure and radially outward of and adjacent the radial ply structure. The underlay structure is comprised of a single flat strip of material disposed in a plurality of spaced apart circumferential windings about the tire carcass. The flat strip is comprised of a plurality of high modulus, essentially inextensible cords embedded more or less parallel to one another within an elastomeric matrix and a beam made of elastomeric material that is contiguous with the elastomeric matrix in which the high modulus essentially inextensible cords are embedded. The high modulus, essentially inextensible cords are made of a material selected from a group of materials exemplified by nylon, rayon, polyester, aramid, glass and metal. The overall lateral width of the underlay structure is less than the lateral width of the breaker structure. The plurality of essentially inextensible cords embedded within the elastomeric material of the underlay structure may or may not be cut at regular intervals of between about 10 cm and 20 cm in order to enable the underlay strip to accommodate the blown up of the green tire carcass into the toroidal carcass shape. The cords are cut if the blow up change in diameter of the underlay strip is greater than the limited extensibility of the cord. The beam is made of elastomeric material having a modulus of elasticity that is equal to or greater than the modulus of elasticity of the elastomeric material within which the essentially inextensible cords are embedded. The beam has a thickness of between about 1 mm and 10 mm and most preferably a thickness of between about 3 mm and 7 mm. The beam portion of the underlay structure is positioned radially inward of the main body of the underlay structure or radially outward of the main body of the underlay structure.
In a third embodiment, the present invention relates to a pneumatic radial ply tire having a tread, a carcass with two sidewalls, two inextensible annular beads, a radial ply structure, a belt structure located between the tread and the radial ply structure, and an air impermeable innerliner. The tire has a crown stiffening underlay structure disposed radially inward of and adjacent the radial ply structure and radially outward of and adjacent the innerliner. The underlay structure is comprised of a single flat strip of material disposed in a plurality of spaced apart, circumferential windings about the tire carcass. The flat strip is comprised of a plurality of high modulus essentially inextensible cords embedded more or less parallel to one another within an elastomeric matrix. The high modulus essentially inextensible cords are made of a material selected from a group of materials exemplified by nylon, rayon, polyester, arimid, metal and glass. The overall lateral width of the underlay structure is less than the lateral width of the breaker structure. The plurality of essentially inextensible cords embedded within the elastomeric material of the underlay structure may or may not be cut at regular intervals of between about 10 cm and 20 cm in order to enable the underlay strip to accommodate the blown up of the green tire carcass into the toroidal carcass shape. The cords are cut if the blow up change in diameter of the underlay strip is greater than the limited extensibility of the cord.
In another embodiment, the present invention relates to a pneumatic radial ply tire having a tread, a carcass with two sidewalls, two inextensible annular beads, a radial ply structure, a belt structure located between the tread and the radial ply structure, and an air impermeable innerliner. The tire has a crown stiffening underlay structure disposed radially inward of and adjacent the radial ply structure and radially outward of and adjacent the innerliner. The underlay structure includes a single flat strip of material disposed in a plurality of spaced apart circumferential windings about the tire carcass. The flat strip includes a plurality of high modulus essentially inextensible cords embedded more or less parallel to one another within an elastomeric matrix and a beam made of elastomeric material that is contiguous with the elastomeric matrix in which the high modulus essentially inextensible cords are embedded. The high modulus essentially inextensible cords are made of a material selected from a group of materials exemplified by nylon, rayon, polyester, aramid, glass and metal. The overall lateral width of the underlay structure is less than the lateral width of the breaker structure, and the plurality of essentially inextensible cords embedded within the elastomeric material of the underlay structure may or may not be cut at regular intervals of between about 10 cm and 20 cm, most preferably at about 15 cm intervals in order to enable the underlay strip to accommodate the blown up of the green tire carcass into the toroidal carcass shape. The cords are cut if the blow up change in diameter of the underlay strip is greater than the limited extensibility of the cord. The beam is made of elastomeric material having a modulus of elasticity that is equal to or greater than the modulus of elasticity of the elastomeric material within which the essentially inextensible cords are embedded, and it has a thickness of between about 1 millimeter and 10 mm and most preferably a thickness of between about 3 mm and 7 mm. The beam portion of the underlay structure might be positioned radially inward of the main body of the underlay structure, or radially outward of the main body of the underlay structure.